EP-A-0 076 744, EP-A-0 284 345, U.S. Pat. No. 3,643,851 and U.S. Pat. No. 4,179,057 disclose surgical clips which are of simple U-shape, when undeformed prior to use, and are, therefore, most economical to produce. Such U-clips provide effective adaptation and eversion of the margins of a wound to be closed. A disadvantage of such clips is, however, that their cutting edges, upon seizing the margins of a wound when the clip is being implanted, tend to tear open traumatic channels in the skin and tissue, in which inflammation can occur. Also the clip tends to destroy tissue, as the clip splays apart upon its removal, so as to open regions of the wound which have already healed.
So called "D clips" which are of D-shape in their fully deformed condition are disclosed in DE-A-2 625 991, DE-A-3 204 532, U.S. Pat. No. 1,910,688 and U.S. Pat. No. 4,321,002, which yield better results insofar as the above described disadvantages are concerned. An essential feature of such a clip is that the legs of the clip are of arcuate shape with a view to ensuring that they form atraumatic puncture channels upon implantation.
It has been found, however, that "D clips" have a major disadvantage in clinical practice For good scar formations, a wound should begin to heal from the lower layer (stratum germinativum) of the epidermis, and for it to extend without bridging over malformations. Also the juxtaposition of the corium as middle skin layer and the lowermost skin layer or subcutis should, as far as possible be tension-free. To this end, the surgeon first spreads the upper skin layers at the margins of the wound to form a V-shaped parting with the point of the V in the region of the closely joined lower stratum germinativum. Since this position of the wound margins, which is known as eversion, must be maintained for some days after the closure of the wound, said position is fixed by means of a stitch. It has been found, however, that when "D clips" are used the desired eversion is not maintained, because the curved legs of the clip cannot develop sufficient retaining forces in the tissue so that the margins of the wound tend to ride up the legs of the clip. So long, however, as both margins ride up the legs of the clip to an equal extent, the resultant effect, although not desired, is normally tolerable in so far as the healing of the wound is concerned and shows up as a relatively wide scar formation.
If, however, the margins of the wound are displaced in opposite directions, or to different extents, on the legs of the clip, the margins of the wound will form a step as they heal, so that the resulting scars will be conspicuous. Since the three upper skin layers will be out of alignment with each other, the organism will itself even out the skin layers so that a relatively wide scar is produced.
In the light of the foregoing it may be said that "U-clips" cannot be implanted or removed without trauma, but are otherwise capable of maintaining eversion of the margins of the wound and that although "D clips" can in general be used without trauma, they fail to provide lasting eversion of the margins of the wound.
Both "U clips" and "D clips" have the further disadvantage that are not compatible with variations of the margins of a wound. Especially in the case of orthopedic operations, for example the implanting of artificial hip joints, the margins of the wound are subjected to severe mechanical stress by the instrumentation and, therefore, become more swollen than the margins of normal skin incisions. By reason of such swelling the legs of an implanted clip are forced apart by the pressure of the tissue so that the clip, and thus the wound, are partially reopened.